Object Oriented Prograring(OOP) java
- 2. 2 Quetion::explain the five way of creating object in java ● Different ways to create objects in Java As you all know, in Java, a class provides the blueprint for objects, you create an object from a class. There are many different ways to create objects in Java. Following are some ways in which you can create objects in Java:
- 3. 3 1) Using new Keyword ● 1) Using new Keyword : Using new keyword is the most basic way to create an object. This is the most common way to create an object in java. Almost 99% of objects are created in this way. By using this method we can call any constructor we want to call (no argument or parameterized constructors).
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- 5. 5 2) Using New Instance 2) Using New Instance : ● If we know the name of the class & if it has a public default constructor we can create an object –Class.forName. We can use it to create the Object of a Class. Class.forName actually loads the Class in Java but doesn’t create any Object. To Create an Object of the Class you have to use the new Instance Method of the Class.
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- 7. 7 3) Using clone() method Using clone() method: ● Whenever clone() is called on any object, the JVM actually creates a new object and copies all content of the previous object into it. Creating an object using the clone method does not invoke any constructor. ● To use clone() method on an object we need to implement Cloneable and define the clone() method in it.
- 8. 8 . Note : 1)Here we are creating the clone of an existing Object and not any new Object. 2)Class need to implement Cloneable Interface otherwise it will throw CloneNotSupportedException.
- 9. 9 4) Using deserialization 4) Using deserialization : ● Whenever we serialize and then deserialize an object, JVM creates a separate object. In deserialization, JVM doesn’t use any constructor to create the object. ● To deserialize an object we need to implement the Serializable interface in the class.
- 10. 10 Serializing an Object :
- 11. 11 Deserialization of Object : Object of DeserializationExample class is serialized using writeObject() method and written to file.txt file.
- 12. 12 5 Factory Method: ● Factory method is a creational design pattern, i.e, related to object creation. In Factory pattern, we create object without exposing the creation logic to client and the client use the same common interface to create new type of object. The idea is to use a static member-function (static factory method) which creates & returns instances, hiding the details of class modules from user. ● A factory pattern is one of the core design principles to create an object, allowing clients to create objects of a library(explained below) in a way such that it doesn’t have tight coupling with the class hierarchy of the library. WHAT IS MEANT WHEN WE TALK ABOUT LIBRARY AND CLIENTS? ● A library is something which is provided by some third party which exposes some public APIs and clients make calls to those public APIs to complete its task. A very simple example can be different kinds of Views provided by Android OS.
- 13. 13 public class User { private static volatile User instance = null; // other fields / standard constructors / getters public static User getSingletonInstance(String name, String email, String country) { if (instance == null) { synchronized (User.class) { if (instance == null) { instance = new User(name, email, country); } } } return instance; } } User user = User.getSingletonInstance("John", "[email protected]", "Argentina");